1. Technical Field
The present invention relates to a driving apparatus of a plasma display panel (PDP) and a method for displaying pictures on the plasma display panel and, more particularly, to a driving apparatus of a plasma display panel (PDP) and a method for displaying pictures on the plasma display panel with increased ability to express a low gray scale.
2. Related Art
Recently, flat panel displays, such as liquid crystal displays (LCDs), field emission displays (FEDs) and PDPs, have been actively developed. The PDPs are advantageous over the other flat panel displays with respect to their high luminance, high luminous efficiency and wide viewing angle. Accordingly, the PDPs are being highlighted as a substitute for conventional cathode ray tubes (CRTs) for large-screen displays of more than 40 inches in size.
The PDPs are flat panel displays that use plasma generated by gas discharge to display characters or images. The PDPs include, according to their size, more than several tens to millions of pixels arranged in the form of a matrix. These PDPs are classified into a direct current (DC) type and an alternating current (AC) type according to patterns of waveforms of driving voltages applied thereto and discharge cell structures thereof.
The direct current plasma display panel (DC PDP) has electrodes exposed to a discharge space, thereby causing current to directly flow through the discharge space during application of a voltage to the DC PDP. In this connection, the DC PDP has a disadvantage in that it requires a resistor for limiting the current. On the other hand, the alternating current plasma display panel (AC PDP) has electrodes covered with a dielectric layer that naturally forms a capacitance component to limit the current and protects the electrodes from the impact of ions during a discharge. As a result, the AC PDP is superior over the DC PDP in that it has a longer life than the DC PDP.
In an AC PDP, scan electrodes and sustain electrodes covered with a dielectric layer and a protective layer are arranged in pairs in parallel on a first glass substrate. A plurality of address electrodes covered with an insulation layer is arranged on a second glass substrate. Barrier ribs are formed in parallel with the address electrodes on the insulation layer such that each barrier rib is interposed between adjacent address electrodes. A phosphor is coated on the surface of the insulation layer and on both sides of each partition wall. The first and second glass substrates are arranged to face each other while defining a discharge space therebetween so that the address electrodes are orthogonal to the scan electrodes and sustain electrodes. In the discharge space, a discharge cell is formed at an intersection between each address electrode and each pair of scan electrodes and sustain electrodes.
The electrodes of the PDP are arranged in the form of an m×n matrix. In detail, m address electrodes are arranged in a column direction. Also, n scan electrodes and n sustain electrodes are alternately arranged in a row direction.
In general, a process for driving the AC PDP can be expressed by temporal operation periods, i.e., a reset period, an address period and a sustain period.
The reset period is a period in which the state of each cell is initialized so that an addressing operation of each cell is smoothly performed, and the address period is a period in which an address voltage is applied to an addressed cell so as to accumulate wall charges on the addressed cell in order to select a cell to be lighted and a cell not to be lighted in the PDP. The sustain period is a period in which sustain pulses are applied to the addressed cell, thereby performing a discharge according to which a picture is actually displayed.
In the PDP, a gray scale is expressed by dividing one frame (1 TV frame) into a plurality of sub-fields, and performing a time-division operation for the plurality of sub-fields. Each sub-field comprises the reset period, the address period and the sustain period, which have been mentioned above. One frame is divided into 8 sub-fields in order to express 256 gray scales, and each sub-field comprises reset periods, address periods and sustain periods. The sustain periods have lighting periods in a ratio of 1:2:4:8:16:32:64:128.
In the sub-field arrangement, the minimal gray scale which can be implemented is 1, that is, there is a limit to expression of gray scale below 1. If the number of sub-fields is increased so as to generate 512 gray scales for expressing the low gray scale, a problem may arise in that the sustain period is decreased as the address period is increased, which results in low brightness. Accordingly, the above-described methods have problems in expressing the low gray scale (for example, 0.5 or 0.25 gray scale and the like) without increasing the number of sub-fields.